1. Field of the Invention
The present invention relates to a detection apparatus and, more particularly, to a detection apparatus for detecting the characteristics of a sample by making use of a surface plasmon resonance.
2. Description of the Related Art
Conventionally, a surface plasmon sensor is known as a detection apparatus for detecting the characteristics of a sample by making use of the surface plasmon resonance (SPR). Generally, the surface plasmon sensor is constituted by: a prism; a metallic thin film layer arranged on a surface of the prism for fixing a physiologically active substance as the sample; a light source for emitting a light beam; an optical system for making the light beam incident at various angles to the prism so that total reflection conditions may be satisfied on the interface between the prism and the thin film layer; and a photodetector for detecting the light intensity distribution of the light beam totally reflected at the interface. The characteristics of the physiologically active substance are analyzed by detecting the position, at which the dark line is formed by the total reflection attenuation due to the surface plasmon resonance, from the light intensity distribution detected by the photodetector.
As a technique for detecting the position of the dark line, in Japanese Patent Application Laid-Open (JP-A) No. 2006-98369, a technique is disclosed for detecting the position of the dark line highly precisely by storing in advance the light intensity distribution of a light beam having no total reflection attenuation itself, as a reference light intensity distribution, detecting the light intensity distribution of the light beam totally reflected at the interface, and dividing the detected light intensity distribution for each distribution value by the reference light intensity distribution, so that the influence of the dispersion of the light intensity distribution of the light beam is offset.
In JP-A No. 2003-14623, a technique is disclosed for detecting the position of a total reflection attenuation angle highly precisely by storing in advance an equation of a plasmon resonance curve expressing the relation between a reflectance and an incidence angle, and by fitting the plasmon resonance curve, as expressed by the equation, for the light intensity distribution of the light beam detected.
Here in a detection apparatus of this type, noise is generated in the light beam due to dust stuck to the prism or by flaws in the optical paths of the optical system. This results in a decrease in the precision of detection of the dark line position.
However, in the techniques thus far described, the situation in which noise occurs in the light beam has not been taken into consideration and there is the problem that it is impossible to detect the decrease in the precision of detection of the dark line position.